Rename source files

- Rename passqr to passqr.sh and unset executable flag
- Rename password-store-qr to passqr.bash-completion

The make script will still install them to the same respective locations.
Remove unnecessary PKGNAME from makefile
Use @install -v in makefile

Now make will not output the install commands, instead install will
output what it is doing.
Add uninstall make target